The present invention relates to a circuit breaker covering a breaker such as a molded-case circuit breaker or a ground leakage breaker.
As is well known, the above-described circuit breaker is made up of contactor sections, each corresponding to each phase in a main circuit as a multi-phase circuit and including a stationary contactor and a movable contactor, arc-extinguishing devices for the respective contactor sections, a switching mechanism driving the movable contactors for switching, a tripping mechanism for the switching mechanism, and an overcurrent tripping device actuating the tripping mechanism by detecting an overcurrent, which are assembled together in a molded case (see, for example, JP-A-5-211024).
In the circuit breaker with the above arrangement, interruption of an overcurrent such as a short-circuit current causes an arc to occur between a stationary contact and a movable contact in the main circuit. The heat of the arc causes metals of materials of the contacts to melt and evaporate. The evaporated molten metals are scattered around with an arc gas to be deposited on movable parts of the switching mechanism and the tripping mechanism, which sometimes causes deterioration in the function of their interruption action. Moreover, an arc gas, produced at current interruption, spreading over poles and flowing in between the poles causes a decrease in interphase breakdown strength to also cause a problem of making it impossible to obtain a high interruption performance. Particularly in a ground leakage breaker, a zero-phase current transformer in a leakage current detection section is contained in the molded case while being arranged next to the back of contactor sections in all poles. This structurally makes it difficult to isolate the poles from one another, by which the arc gas is liable to go around between the poles through the containing space.
About this, the following structure is known as a measure for preventing molten metals, produced at contactor sections at interruption of an overcurrent and scattered around, from being deposited on mechanisms such as a switching mechanism (see, for example, JP-X-2001-41168). In the structure, a contactor section and an arc-extinguishing device for each of the poles are contained in an independently provided arc-extinguishing chamber case enclosing them to be provided as a unit. With the unit being contained in a molded case of a circuit breaker together with other units to make the poles isolated from one another, a switching mechanism is made linked with a movable contactor in each of the units in the molded case.
In addition to the structure disclosed in JP-X-2001-41168, there is known a circuit breaker having a simple assembly structure for ensuring the shielding of a switching mechanism from molten metals scattered around by heat of an arc. In the assembly structure, a molded case of the circuit breaker is made to have a structure being dividable into a main case (a lower case), a middle cover laid on the top of the main case, and a top cover covering the top of the middle cover. The main case contains contactor sections, arc-extinguishing devices, and an overcurrent tripping device. The middle cover has a recess, partitioned with a wall, formed in the central section thereof to contain the switching mechanism and a tripping mechanism in the recess.
The above-described circuit breakers with related structures have the following problems. In the assembly structure disclosed in JP-X-2001-41168, the isolated arc extinguishing-chamber case, which is independently prepared for each pole and mounted in the molded case, increases the number of assembled parts and man-hours for assembly, which results in an increased cost. In the arrangement in which the molded case is made to have a dividable structure, the switching mechanism, being contained in the recess in the middle cover to be isolated from the contactor sections and the arc-extinguishing devices, can only be prevented from the molten metals, scattered around from the contactor sections along with current interruption, depositing on the switching mechanism. The arrangement as it is, however, provides a space, containing the overcurrent tripping device and the zero-phase current transformer of the ground leakage breaker arranged next to the back of the contactor sections in the main case, as a circuitous path for an arc gas produced at current interruption. Therefore, the arrangement can not solve the problem yet in which an arc gas produced at current interruption goes around between poles to cause a decrease in interphase breakdown strength.
The present invention was made in view of the foregoing with an object of providing a circuit breaker in which the structure of a molded case is improved so as to inhibit deterioration in interphase insulation due to a going around arc gas to enhance interruption performance and reliability of the circuit breaker.
Further objects and advantages of the invention will be apparent from the following description of the invention and the associated drawings.